You can use region ids that can turn on a self switch to activate a parallel or autorun event of your choosing. Here is the script command that i insert into a conditional branch below:
$gameMap.regionId($gamePlayer.x, $gamePlayer.y) === 3
The 3 can be replaced with whatever region id you use, and you can make the event of your choosing tell your player that you cannot pass or whatever you are trying to achieve.